# Claude Code v2.1.165

> Claude Code v2.1.165, released 5 Jun 2026 (2026-06-05). 2 entries read out of the shipped bundle. Unofficial, and not affiliated with Anthropic.

Web version: https://changelogs.core-directive.com/v/2.1.165

This is a small patch release built one day after v2.1.163. The two notable functional changes are: conversation summarization can now use extended thinking when the active model supports it (controlled by a server-side capability list), and subagent API calls are now tagged in the billing attribution header.

## Changes

### Extended Thinking Support in Conversation Summarizer

Previously the summarizer that compresses long conversations always ran with `thinkingConfig: { type: "disabled" }`, regardless of what model was active. In this version a new capability check is evaluated at summarization time: if the current main-loop model is listed in the server-side `cedar_lagoon` capability map, the summarizer now inherits the same thinking configuration used by the main conversation loop. For models that are not in the list, the old behavior (thinking disabled) is unchanged.

In practice this means users running a model that supports extended thinking may notice more coherent or accurate conversation compaction when context windows fill up, since the summarizer can now reason before producing the summary.

**Evidence**

New capability gate function (searches `clientDataCache?.cedar_lagoon`); summarization call site changed from hardcoded `{ type: "disabled" }` to `hM8(K.options.mainLoopModel) ? K.options.thinkingConfig : { type: "disabled" }` — search for `"cedar_lagoon"` to locate the check.

### Subagent Sessions Identified in Billing Attribution Header

The `x-anthropic-billing-header` sent with every API request now includes `cc_is_subagent=true;` when the request originates from a subagent session rather than the top-level interactive session. The main CLI session is tagged `isMainSession: true` internally; any agent that lacks that flag gets the subagent marker appended.

This is an internal attribution change with no user-visible behavior. It helps Anthropic distinguish API usage generated directly by the user from usage generated by orchestrated subagents, which improves billing analytics and usage reporting.

**Evidence**

Attribution header builder now appends `cc_is_subagent=true;` for non-main-session callers (search for `"cc_is_subagent=true;"` in the source); main session agent config now sets `isMainSession: !0`.